The present invention relates to a solid-state image sensing device and, in particular, to a CMOS (Complementary Metal Oxide Semiconductor) image sensor.
In the solid-state image sensing device, photodiodes are arranged two-dimensionally. In a case of the CMOS image sensor, generally, exposure and reading are performed line-by-line basis. Therefore, when imaging a subject or the like which is rotating at a high speed using the CMOS image sensor, a captured imaged tends to suffer a distortion. Such a phenomenon is known as a rolling shutter.
On the other hand, in a case of a CCD (Charge Coupled Device) image sensor, exposure and reading are performed on a frame-by-frame basis. Therefore, when the CCD image sensor is used, even if the subject is rotating at a high speed, the captured image does not suffer a distortion. Such a phenomenon is known as a global shutter.
In the CMOS image sensor also, there is a case where the global shutter operation is required. As a system for realizing the global shutter operation in the CMOS image sensor, there is one disclosed, for example, in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2012-129797).
The CMOS image sensor described in Patent Document 1 has a substrate. The substrate has a main surface and a back surface. In the substrate, a photodiode, a charge holding part, and a floating diffusion region are formed. The charge holding part has a p type region on the side of the main surface. Over the main surface, a gate insulating film is formed. Over the gate insulating film, a first transfer gate and a second transfer gate are formed.
In the CMOS image sensor disclosed in Patent Document 1, incident light is converted into an electric charge by the photodiode through photoelectric conversion. The charges photo-electrically converted in the photodiode are transferred for all unit pixels simultaneously to the charge holding part through the first transfer gate. Then, the charges are read sequentially on a row-by-row basis by the second transfer gate. Thus, the CMOS image sensor disclosed in Patent Document 1 realizes the global shutter operation.